Loans and Leases (Details 2) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Financing Receivable, Impaired [Line Items]
Nonaccrual	$ 99,113	$ 79,333
Loans held for investment	18,735,543	17,957,713
Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		79,333
Loans held for investment	18,735,543	17,957,713	$ 17,230,146
Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	18,636,430
Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		17,878,380
Real Estate Mortgage
Financing Receivable, Impaired [Line Items]
Nonaccrual	22,383
Loans held for investment	7,896,924	7,918,141
Real Estate Mortgage | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		17,845
Loans held for investment	7,896,924	7,918,141	7,678,660
Real Estate Mortgage | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	7,874,541
Real Estate Mortgage | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		7,900,296
Real Estate Mortgage | Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual	19,515
Loans held for investment	4,300,566	4,824,298
Real Estate Mortgage | Commercial | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		15,321
Loans held for investment		4,824,298
Real Estate Mortgage | Commercial | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	4,281,051
Real Estate Mortgage | Commercial | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		4,808,977
Real Estate Mortgage | Residential Real Estate
Financing Receivable, Impaired [Line Items]
Nonaccrual	2,868
Loans held for investment	3,596,358	3,093,843
Real Estate Mortgage | Residential Real Estate | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		2,524
Loans held for investment		3,093,843
Real Estate Mortgage | Residential Real Estate | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	3,593,490
Real Estate Mortgage | Residential Real Estate | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		3,091,319
Real Estate Construction and Land
Financing Receivable, Impaired [Line Items]
Nonaccrual	377
Loans held for investment	2,551,474	2,233,656
Real Estate Construction and Land | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		442
Loans held for investment	2,551,474	2,233,656	2,000,957
Real Estate Construction and Land | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	2,551,097
Real Estate Construction and Land | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		2,233,214
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable
Financing Receivable, Impaired [Line Items]
Nonaccrual	377
Loans held for investment	1,009,362	912,583
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		442
Loans held for investment		912,583
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	1,008,985
Real Estate Construction and Land | Commercial Real Estate Construction Loan Receivable | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		912,141
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable
Financing Receivable, Impaired [Line Items]
Nonaccrual	0
Loans held for investment	1,542,112	1,321,073
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		0
Loans held for investment		1,321,073
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	1,542,112
Real Estate Construction and Land | Residential Real Estate Construction Financing Receivable | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		1,321,073
Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual	75,700
Loans held for investment	7,878,557	7,404,595
Commercial | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		60,003
Loans held for investment	7,878,557	7,404,595	7,152,058
Commercial | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	7,802,857
Commercial | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		7,344,592
Commercial | Asset-based
Financing Receivable, Impaired [Line Items]
Nonaccrual	33,015
Loans held for investment	3,810,741	3,305,421
Commercial | Asset-based | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		32,324
Loans held for investment		3,305,421
Commercial | Asset-based | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	3,777,726
Commercial | Asset-based | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		3,273,097
Commercial | Venture Capital Loans
Financing Receivable, Impaired [Line Items]
Nonaccrual	20,131
Loans held for investment	2,209,649	2,038,748
Commercial | Venture Capital Loans | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		20,299
Loans held for investment		2,038,748
Commercial | Venture Capital Loans | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	2,189,518
Commercial | Venture Capital Loans | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		2,018,449
Commercial | Other Commercial
Financing Receivable, Impaired [Line Items]
Nonaccrual	22,554
Loans held for investment	1,858,167	2,060,426
Commercial | Other Commercial | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		7,380
Loans held for investment		2,060,426
Commercial | Other Commercial | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	1,835,613
Commercial | Other Commercial | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		2,053,046
Consumer
Financing Receivable, Impaired [Line Items]
Nonaccrual	653
Loans held for investment		401,321
Consumer | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Nonaccrual		1,043
Loans held for investment	408,588	401,321	$ 398,471
Consumer | Performing
Financing Receivable, Impaired [Line Items]
Loans held for investment	$ 407,935
Consumer | Performing | Non Purchased Credit Impaired Loans and Leases
Financing Receivable, Impaired [Line Items]
Loans held for investment		$ 400,278